The ability to monitor the concentration of oxygen in gases flowing in and out of the patient's lungs would be of invaluable assistance to the medical profession. Instruments for measuring the concentration of oxygen are available, but none has all the characteristics required, namely, a fast speed of response, sufficient accuracy and stability, freedom from malfunction in the presence of water vapor and other extraneous matter and the ability to operate in a stream of gas.
It has been suggested that concentration of oxygen can be determined by measuring the absorption of U.V. light, but this can result in the production of ozone in harmful quantities unless, as suggested by myself and Robert Chaney, all but one narrow emission band of U.V. light is filtered out. Unfortunately, the water vapor and other gases such as CO.sub.2 usually present in the patient's breath also absorb the U.V. light of the selected narrow emission band so that their concentration must be determined by other instruments before the absorption due to the oxygen alone can be identified.